| Message ID | 1492132420-70400-1-git-send-email-gfree.wind@foxmail.com |
|---|---|
| State | Not Applicable |
| Delegated to: | Pablo Neira |
| Headers | show |
On Fri, Apr 14, 2017 at 09:13:40AM +0800, gfree.wind@foxmail.com wrote: > From: Gao Feng <fgao@ikuai8.com> > > The function ctnl_untimeout is used to untimeout every conntrack > which is using the timeout. But it is necessary to add one barrier > synchronize_rcu because of racing. Maybe one conntrack has already > owned this timeout, but it is not inserted into unconfirmed list or > the hash list, when ctnl_untimeout untimeout the conntracks > > Let me describe it with a call path > CPU1 CPU2 > alloc new conn > add timeout ext > ctnl_timeout_try_del > untimeout all conns in list > kfree_rcu. > conn is confirmed. Then this confirmed conn gets a timeout_ext->timeout == NULL since ctnl_untimeout() is called first. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> From: Pablo Neira Ayuso [mailto:pablo@netfilter.org] > On Fri, Apr 14, 2017 at 09:13:40AM +0800, gfree.wind@foxmail.com wrote: > > From: Gao Feng <fgao@ikuai8.com> > > > > The function ctnl_untimeout is used to untimeout every conntrack which > > is using the timeout. But it is necessary to add one barrier > > synchronize_rcu because of racing. Maybe one conntrack has already > > owned this timeout, but it is not inserted into unconfirmed list or > > the hash list, when ctnl_untimeout untimeout the conntracks > > > > Let me describe it with a call path > > CPU1 CPU2 > > alloc new conn > > add timeout ext > > ctnl_timeout_try_del > > untimeout all conns in list > > kfree_rcu. > > conn is confirmed. > > Then this confirmed conn gets a timeout_ext->timeout == NULL since > ctnl_untimeout() is called first. The new conn gets the timeout_ext->timeout before ctnl_untimeout, when add the timeout ext. Then ctnl_untimeout happens before the new conn is inserted into unconfirmed list. It could not reset the timeout pointer of new conn to NULL. Maybe I should add the "insert unconfirm list" in the call path. I could not understand why the conn gets one NULL pointer, not invalid pointer in this case. Regards Feng -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c index 47d6656..af0cc87 100644 --- a/net/netfilter/nfnetlink_cttimeout.c +++ b/net/netfilter/nfnetlink_cttimeout.c @@ -304,6 +304,11 @@ static void ctnl_untimeout(struct net *net, struct ctnl_timeout *timeout) spinlock_t *lock; int i, cpu; + /* Make sure the conntrack using the timeout already in the unconfirmed + * list or in the hash table. + */ + synchronize_rcu(); + for_each_possible_cpu(cpu) { struct ct_pcpu *pcpu = per_cpu_ptr(net->ct.pcpu_lists, cpu);